The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known powertrain architectures include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. One exemplary powertrain includes a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Electric machines, operative as motors or generators, generate a torque input to the transmission, independently of a torque input from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.
Operation of the above devices within a hybrid powertrain vehicle require management of numerous torque bearing shafts or devices representing connections to the above mentioned engine, electrical machines, and driveline. Input torque from the engine and input torque from the electric machine or electric machines can be applied individually or cooperatively to provide output torque. Various control schemes and operational connections between the various aforementioned components of the hybrid drive system are known, and the control system must be able to engage to and disengage the various components from the transmission in order to perform the functions of the hybrid powertrain system. Engagement and disengagement are known to be accomplished within the transmission by employing selectively operable clutches.
Clutches are devices well known in the art for engaging and disengaging shafts including the management of rotational velocity and torque differences between the shafts. Clutches are known in a variety of designs and control methods. One known type of clutch is a mechanical clutch operating by separating or joining two connective surfaces, for instance, clutch plates, operating, when joined, to apply frictional torque to each other. One control method for operating such a mechanical clutch includes applying a hydraulic control system implementing fluidic pressures transmitted through hydraulic lines to exert or release clamping force between the two connective surfaces. Operated thusly, the clutch is not operated in a binary manner, but rather is capable of a range of engagement states, from fully disengaged, to synchronized but not engaged, to engaged but with only minimal clamping force, to engaged with some maximum clamping force. The clamping force available to be applied to the clutch determines how much reactive torque the clutch can carry before the clutch slips.
The hydraulic control system, as described above, utilizes lines charged with hydraulic oil to selectively activate clutches within the transmission. However, the hydraulic control system is also known to perform a number of other functions in a hybrid powertrain. For example, an electric machine utilized within a hybrid powertrain generates heat. Known embodiments utilize hydraulic oil from the hydraulic control system in a continuous flow to cool the electric machine in a base machine cooling function. Other known embodiments additionally are known to react to higher electric machine temperatures with a selectable or temperature driven active machine cooling function, providing additional cooling in the high temperature condition. Additionally, known embodiments utilize hydraulic oil to lubricate mechanical devices, such as bearings. Also, hydraulic circuits are known to include some level of internal leakage.
Hydraulic oil is known to be pressurized within a hydraulic control system with a pump. The pump is preferably mechanically driven. In addition to this first main hydraulic pump, hydraulic control systems are known to also include an auxiliary hydraulic pump, preferably powered electrically and used when the mechanically driven pump is unavailable. The internal impelling mechanism of a pump rotates or operates at some speed, drawing hydraulic oil from a return line and pressurizing the hydraulic control system. The supply of hydraulic flow by the pump or pumps is affected by the speed of the pumps, the back pressure exerted by the hydraulic line pressure (PLINE), and the temperature of the hydraulic oil (TOIL).
Selective application of a flow of hydraulic fluid to functions served by the hydraulic control system requires valves or switches to apply or release the flow to the functions. Hydraulic valves are known in a variety of configurations in the art. Two known configurations include an electrically-actuated pressure control solenoid (PCS), wherein a valve internal to the PCS is translated, rotated, or otherwise moved by electromagnetic-mechanical means and is capable of a plurality or linearly variable actuation providing some fraction of a supplied line pressure; and a hydraulically-actuated flow management valve, wherein a valve internal to the flow management valve is translated, rotated, or otherwise moved by selective application of a command pressure and actuates between distinct states, for example, between two positions.
Utilizing a series of PCS valves and flow management valves to control a powertrain through complex operations can be difficult. A separate switch can be assigned to each individual function served by the hydraulic control system. However, such a system can be cost prohibitive and create increasing warranty concerns. Multi-level control systems are known, wherein a first set of valves controls flow to a second set of valves, and the multiplicity of settings between the different levels of valves can serve multiple functions with fewer physical valves. However, this coordinated valve action requires careful control, as a delay in actuation of a valve or some other malfunction can create unexpected or undesirable results in the operation of the powertrain.
A method to control multi-level hydraulic control valves within a transmission, insuring timely and accurate control of the functions served by the valves, would be beneficial.